Delivery form and storage

The TROSIFOL film layers stick together on the film roll in spite of the film’s rough surface. This is known as blocking (= sticking together on each other). Various counter-measures can be taken to prevent blocking which, otherwise, would make it impossible to process the PVB film.

One possibility is to wind in an appropriate plastic separating film - in this case preferably a thin embossed PE interleaved film. This process was developed and patented by TROSIFOL and finds widespread use nowadays. Another method is to cool the film down to a temperature of 8°C (46°F) or lower. This greatly diminishes the adhesive (blocking) behaviour of the film for problem-free handling. However, the latter method consumes a great deal of energy and is therefore cost intensive. Both delivery forms are discussed in the following chapters.

TROSIFOL with PE interleaved film

TROSIFOL with PE interlayer For TROSIFOL with PE interlayer, the undesirable adhesion of the film surface to itself is prevented by interleaving the individual TROSIFOL layers with an embossed PE film. In its original packaging, TROSIFOL with PE interlayer can be stored in any normal,dry room. TROSIFOL with PE interlayer in its original heat-sealed PE bags has a usual storage life of at least three years without loss of quality. However, TROSIFOL with PE interlayer in its factory-sealed packaging should not be stored at temperatures in excess of 30°C (86°F). Keeping the product in a refrigerated store at approx. 8°C (46°F) is also possible. Rolls which have been opened and started to use may be stored in a climatized room. This is particularly advantageous when small numbers of windscreens of different types have to be manufactured or when - in the production of flat laminated safety glass for architectural applications - the sizes are such that a full TROSIFOL roll cannot be used at one time. TROSIFOL as refrigerated film When PVB is wound, stored or transported at temperatures below 8°C (46°F), there is no need to use a seperating agent to keep the layers of film apart on the roll. This advantage is available with TROSIFOL refrigerated film, which is transported in special refrigerated trucks and should be stored at temperatures of 8°C. The relative humidity need not generally be controlled with this film type. However, once a roll refrigerated film has been allowed to warm up to a temperature of 12°C (54°F) or more for an extended period of time, it will often be impossible to unroll it without damaging the product. The individual film layers will adhere firmly to each other, even if the film is subsequently cooled down. In the warmer atmosphere of the lay-up room, refrigerated film must be fully unrolled and used, or at least cut into sheets, after no more than 2 to 3 hours.

 

TROSIFOL as refrigerated film

PVB film is wound into rolls at temperatures of ≤ 8°C (46° F) for storage and transportation. This property is utilized by TROSIFOL refrigerated film that is transported in special refrigerated lorries. TROSIFOL refrigerated film is stored in the original package at ≤ 8°C (≤ 46° F), usually under uncontrolled humidity conditions. Refrigerated film rolls stored for extended periods at temperatures of > 8°C (> 46° F) often cannot be unwound without damaging the film. Even renewed cooling down to lower temperatures still does not ensure damagefree separation of the individual film layers. When stored at >8°C (> 46° F) or higher in the laminating room, the refrigerated film rolls must be completely unwound within 2-3 hours and be used or cut to size.

TROSIFOL with PE interleaved film and TROSIFOL refrigerated film only differ by the delivery form and not by the film composition. Consequently, the operating procedure only differs in the preparation of the film and not in the actual lamination process. Compared with refrigerated film, TROSIFOL with PE interleaved film offers the advantage of being able to store opened rolls in air-conditioned lamination rooms. Refrigerated film rolls have to be unwound and used or cut to size before they warm up, whereas rolls of TROSIFOL with PE refrigerated film can be stored in an air-conditioned room at 18 to 20°C (64 to 68° F) and 25 to 30% relative humidity without the individual film layers adhered together and any change of the previously adjusted film moisture of approx. 0.45%. When a film has become a too high moisture level, it must be reconditioned at 25 to 30% relatively humidity prior to application. Under these conditions the customary conditions of approx. 0.4 to 0.5% for processing are once again regained. The film should be freely suspended for reconditioning, either cut to size or as a film strip. Subsequent reconditioning on the roll or as a film stack is not possible or would take a very long time.

Since TROSIFOL already has the required film moisture prior to delivery, lamination between two glass panes can be carried out directly off the roll in an air-conditioned room (18 to 20°C/25 to 30% relative humidity).

TROSIFOL
with PE interleaved film	as refrigerated film/without PE interleaving
Storage in a packed state, without air-conditioning at maximum +30°C (86° F)	Storage and transport refrigerated at ≤ 8°C (≤ 46° F)
Simple storage of left-over rolls in airconditioned lay-up rooms with frequently changing glass ply sizes	Storage of left-over rolls • Tightly sealed bag at ≤ +8°C (≤ 46° F) without controlled room humidity level • Open bag at ≤ +8°C (≤ 46° F) and 25 to 30% relative humidity
Blocking not possible	No PE waste
Film quality is identical for both delivery forms!

When unwinding TROSIFOL film, care must be taken to ensure, that a uniform tension is applied over the entire film width, since stretching of the elastic film would lead to subsequent shrinkage. TROSIFOL with PE interlayer can be unwound with a simple mechanical device (see illustration below).

Fully automatic film cutting and stacking machines can be used when larger quantities of TROSIFOL have to be cut to size for the production of windscreens. These machines permit trapezoid cutting pattern to save considerable quantities of film compared with a rectangular cut. The length is merely increased slightly to compensate for the negligible, production-conditioned shrinkage.

 

 

For small series the film is drawn manually over a back illuminated screen so that the film can be inspected. The film is cut to size on this glass table with a strong and sharp blade. Coloured adhesive strips underneath the table make it easy to maintain the required cut-off length. Rapid unwinding of the PE interleaved film can result in electrostatic charging of the PE film, causing increased risk of contamination of the PVB film. Consequently absolute cleanliness must be assured in conjunction with air ionisers to prevent electrostatic charging. Contact with earthed metal foil strips will also dissipate electrostatic load.

 

When TROSIFOL VG is used as a special, transparent colour-band film in automotive glazing, then the film that is to be prepared for lamination must be cut to size according to the dimensions of the windscreen (W/S) and then stretched, i.e. asymmetrically according to the shape of the windscreen at temperatures in the range between 90-100°C (194-212° F).
The purpose of this pre-treatment operation is to save PVB film trimming waste for more efficient film utilisation in connection with the production of a large number of windscreens and an adaptation of the shaded band to the pane geometry. In some cases stretching is used to eliminate film shrinkage. The following distinctions are made in the subsequently described stretching processes.

 

 

 

 

Stretching in the furnace

• For example clamp 10 film sheets on both sides, left and right, between two rails
• Heat tension free for 20 minutes at 90°C (194° F) in the forced-air furnace
• Trapezoidal pretensioning of the film sheets at the correct angle
• Heat the sheets for 20 minutes at 90°C (194° F)
• Cool down under tension and recondition

 
Stretch by expanding conical rolls (batch cone)

TROSIFOL automotive film is asymmetrically stretched over an expanding conical roll while it is heated to approx.100°C (212° F).

The process is comparatively simple. The disadvantages are the irreversible change of the film surface and subsequent moisture-specific conditioning. Alternatively, the PVB film can be stretched at comparable temperatures over a rigid, non-adjustable conical roll, except that the above-mentioned process disadvantages continue to exist.

The subsequently described continuous stretching processes are far more efficient and economical than the above-described processes.

Stretching with a single cone

With this method the PVB film is continuously stretched over a single cone at an adjustable inclination. The stretching temperature is between 90 and 100°C (194 and 212° F) at a maximum processing speed of 10 m per minute.

The advantages of the process include good adjustability of the stretch radius, a good throughput rate for both transparent and colour-band film. The disadvantages are the comparatively high investment costs, the possible technical thickness fluctuations and the process-related fluctuations of the stretch radius dimensions.

 

 

Stretching processes with multiple cones

In this case several cone rolls of defined inclination arranged behind each other are used for film stretching and subsequent cooling. The radius is altered by changing the position of the film on the cone. The process is more elaborate than working with a single cone and is, therefore, associated with a higher investment.

 

 

 

 

Chemical coating

A metal oxide is coated onto the hot glass surface during the float-glass manufacturing process, thereby establishing a close bond with the glass.

Glass coated in this manner reflects the incoming visible light and can function as heat protection. The surface resistance of this coating is just as high as the actual glass surface.

Physical coating

After the glass has been produced and cut to size, a cathode-ray process (sputtering) coats metal-compounds in various layers onto the glass by vacuum vaporized deposition. The particles are uniformly applied to the glass surface in a continuous process. The coating is more or less durable, depending on the type of metal-compounds used. This type of coating is less durable (corrosion and scratching) than chemical coatings. All these layers can be cleaned by suitable washing machines without fear of damage.

TROSIFOL recommends that the adhesion and competability of the coatings to the PVB has to be checked in advance!

Glass bending utilizes the property that the material does not have a melting point but rather a melting range that varies between 550°C and 560°C (1022 and 1040°F), depending on the glass type. Prefabricated moulds are used and they are covered with refractory textiles on which the glass panes are then placed and softened. Hand-made moulds are used for building glass where quantities and shapes can vary widely, whereas the highest level of simplification and automation has been achieved in the production of glass for motor vehicles where almost all panes are curved. The costly creation of moulds has now been taken over by numerically- controlled machines where shaping is carried out by a computer. A distinction is made between gravity bending and press bending.

Gravity bending

With gravity bending the panes are placed in pairs with a so-called separating agent between the glasses and then exposed to the influence of gravity at temperatures exceeding 600°C (1112°F). The bending process is influenced by the thickness of the glass, the glass dimensions, bending radius and combination variants during the bending process, and thus the tolerances that are usually between 2 and 7 mm.

A continuous process with a gas-flame or electrically heated to approx. 650°C (1200°F), achieves cycles times in the order of 20 seconds per pair of glasses for automotive windscreen production. Another possibility is to use box moulds that are transported through the preheating, bending and cooling zones. The advantages of this method are the programmability of the bending process, the use of different W/S models in one box, and rapid and flexible model changing. Problems that can be associated with gravity bending are due to forced shaping, incorrect alignment or shaping of one or both glasses, undulations during the cooling process. All these factors have an influence on the bending geometry, appearance and laminability of the glass.

Press bending

IIn the press-bending process the glasses are individually raised to a bending temperature of approx. 650°C (1200°F) and then pressed into shape under pressure. The temperature, pressure and bending time must be precisely controlled. The advantages of press bending include high cycle times (approx. 12-15 seconds with W/S), bending of complex pane shapes and efficient handling of very thin glass. As is the case with gravity bending, emphasis must be placed on a neat, temperaturecontrolled cooling process of bending in order to avoid (unwanted) internal stresses in the glass.

The glass must be prepared with maximum care since its condition plays a decisive role in the quality of the finished laminate.

The individual glasses are cut to size from the stock glass sheets to produce the laminated safety glass. A clean cut must be produced because even fine micro-cracks at the edges can be the cause of glass breakage when the laminate is produced. In the event that such faults occur more frequently during the production process, it is advisable to check the glass cutting tools and the actual glass quality.

Since the final laminated glass cannot be bent, the required glasses to produced laminated glass must be paired and bent together. Glasses are cut to size from the stock glass sheets. It is necessary to note that the inside and outside glasses have differing formats. After cutting the glasses to size, either on a machine or manually with the help of templates, the glass edges are finished on a grinding machine or with a diamond wheel. Finally, the glasses are cleaned in a flat-glass washing machine. Modern glass washing machines normally operate horizontally, and they are equipped with rotary brushes to produce a perfectly clean glass surface merely with water. Since the quality of the washing water and the cleanliness of the glass surface influences the adhesion of the PVB film on the glass, only fully demineralised water of ≤ 20 µS (if possible ≤ 5 µS) in the last zone of the washing machine should be used. The effect of the conductivity of the washing water on the adhesion of TROSIFOL film on the glass is indicated by the subsequent graph. In this example a conductivity of approx. 150 µS approximately halves the PVB film adhesion to glass.

Water from natural sources usually contain certain quantities of dissolved salts - mainly the so-called hardness-creating alkaline earth ions such as Ca++ and Mg++ plus Na+ and K+ in lower concentrations. The first two seriously diminish glass adhesion already in low concentrations, whereas the alkaline ions have a hardly measurable influence on the adhesion.

In practice, the removal of the ions through complete demineralisation or reverse osmosis is, therefore, imperative. When mixing completely demineralised water with natural water it is essential that the water hardness, or the specific electrical conductivity, are closely checked before and during the washing process.

When detergents are used in the first washing step to clean particularly dirty glass, then it is essential that completely demineralised water is used for the final rinse before the glass is then dried in a powerful stream of filtered hot air. The air-blowing nozzle should be slanted so that any remaining drops on the back edge of the pane are concentrated in one corner so they can be easily removed.

Washed glass sheets cut to size for windscreens pass through another two additional processing operations before the TROSIFOL film is placed between the two glass sheets. When the glasses have left the glass washing machine a thin layer of bending release agent is uniformly applied so that the paired glass sheets do not stick together at a temperature of approx. 630°C (1165°F) in the bending furnace. E.g. talc or sodium sulphate is used as bending release agent. These substances are dusted onto the glass in a dry state or sprayed on in an aqueous suspension (demineralised water) or solution.

Most bending release agents remaining on the glass surface would invariably impair the optical quality of the windscreens and also adversely influence the adhesion of the film on the glass. It is therefore advisable that all traces of bending release agent should be carefully removed before the TROSIFOL film is applied. The bending release agent can be removed with water in an automatic washing machine or manually. Some bending release agents can be readily removed after the bending process with a powerful industrial vacuum cleaner and a brush.

Laminating room

When different layers of flat and/or curved glass plies - usually in a minimum glass thickness of 3 mm - are laminated with one or more layers of TROSIFOL film, the sheets are almost always cut to size directly from the film roll (except for small formates). For large-formate flat plies up to 3.21 x 6.00 m (so-called jumbo size), sandwich lamination and edge trimming is mainly fully automatic.

Curved glass plies are mainly placed together manually while the actual sandwich is produced by one of the two vacuum processes with a rubber/plastic bag or with rubber ring.

The calander method permits high processing speeds and long production cycles (with minimal ply type changing), and a high degree of automation makes it very efficient. Normally, pre-lamination of the glass/film sandwich is produced in two stages, namely in the pre-nip oven/1st roll pair at approx. 50-70°C (122-158°F) and in the laminating furnace/2nd roll pair at temperatures of approx. 100-120°C (212-248°F) - as indicated in the above diagram.

The segment rolls are arranged horizontally in pairs in the two furnaces. Each roll runs on a separate axle seated on a spring or hydraulic suspension through which the curved glass sandwich is conducted. The processing speed/feeding rate can be automatically programmed in conformity with the complexity of the plies. In individual cases pre-lamination can also be completed with only a single pair of rolls. The temperatures in the infrared heating tunnel are approx. 70-90°C (158-194°F) at a maximum feed speed of 4-5 m/min.

In the two-stage process the glass surface temperature is adjusted by way of the variable speed. Glass temperatures of 50-70°C (122-158°F) are customary in the heating furnace, and 90-110°C (194-230°F) in the second (laminating) furnace. The roll gap is 1 mm narrower than the laminate thickness at a contact pressure of 5-7 bar (73-102 PSI). The operating speed can be increased when the curvature of the plies is not so complex. Greater complexity reduces the possible speed and increases the danger of air bubble formation in the intensely curved area and the trailing edge/rear edge of the ply.

An alternative system to the horizontally arranged segment rolls is the vertical, air-filled calander system ("Lamino" or "Artama"). However, this is only used to bond glasses with a simple curvature at a contact pressure of approx. 3 bar (43 PSI). The process is work intensive, slow and limited to the production of a small number of plies, e.g. for the windscreen replacement market.

The production of the glass pre-laminate by the vacuum process is primarily used for safe deairing of extremely curved (complex) windscreens because even special pre-nip rolls cannot guarantee faultless evacuation of such plies thereby resulting in frequent glass breakage. The working widths of the pre-nip segment rolls are not as wide as very large windscreens, e.g. buses or vans. The vacuum process either uses a rubber bag (Asahi process) rubber gaskets. The laminates evacuated in this manner are heated in a furnace heater with circulated-air. The bags can hold one or more pre-laminates, depending on the given size. Since the rubber bag is easier to fill, this process is also suitable for a continue furnace for large series production at air temperatures of approx. 100-120°C (212-248°F).

Pre-laminate production of large bus plies by the vacuum processes uses especially thin vacuum film bags in a heating cabinet. This process is especially suited for single-piece production. Since the vacuum rubber bags are relatively expensive, another pre-laminate process has been established. The vacuum is drawn with a profile rubber ring that is placed around the glass edge. Plies of differing dimensions require differently sized profile rubber rings. This vacuum process is also suitable for large-series production because the evacuated sandwich is heated under constant vacuum extraction in a continuous tunnel heater with hot circulating air or IR radiation.

With all vacuum pre-lamination processes it is necessary to ensure that evacuation of the positioned pair of plies has almost finished before heating commences (approx. 10 minutes - somewhat longer is even better). This is the only way to avoid incomplete deairing before the edge is sealed. The vacuum must be maintained throughout the heating process (approx. 20 minutes) and should be at least 0.1 to 0.2 bar (- 0.8 to - 0.9 bar/1.5- 3.0 PSI). An ambient air temperature of approx. 100 to 120°C (210 to 250°F) in the heating tunnel or heating cabinet ensures that the necessary glass surface temperature of 95 to 105°C (203 to 221°F) is reached. Pre-laminates produced by a vacuum process are normally clearer than those produced by the calander process. The most favouring processing conditions with regard to temperature and dwell time in the heating tunnel must be established by processing tests. They depend upon the existing equipment.

 

The final laminate is produced in autoclaves that apply a uniform pressure over the entire glass surface. The pre-laminates that are to be autoclaved are prepared in the frame as previously described. There are autoclaves with electrically heated air or heat exchangers. The compressed air can be supplied directly from a compressed-air tank or compressors. The steel cylinder is normally insulated on the inside, but there are also models featuring exterior insulation. The purpose of the pressure process is to ensure complete dissolution of the remaining air and moisture in the molten PVB film. The air is readily dissolved in PVB at the process temperature. The air diffusion speed increases on a linear scale in relation to the pressure, and exponentially with the temperature. PVB adhesion to glass is established as a result of intensive contact. The optimised temperature has a greater effect on final adhesion than the pressure.

The autoclave process consists of 3 phases:

1. Heating

Pressure and temperature are increased parallel.

2. Holding time

The latter is the time during which maximum pressure and maximum temperature prevails on the panes. The adjusted holding time depends on the amount of glass in the autoclave. The holding time should be at least 20 minutes with very thin laminates to ensure that this laminates are pressed for a sufficiently long period at maximum pressure and maximum temperature.

It is necessary to note that, in spite of efficient ventilation, the temperatures at the top of the door are highest, and lowest at the bottom at the back of the autoclave. The pressure during the hold time and the subsequent cooling phase should be approx. 12 bar (175 PSI), and the temperature during the hold time 135 to 145°C (275 to 293°F). The autoclave temperature should be checked every six months with temperature strips located at different positions. This will reveal any differences that exist between the display instrument and the actual internal temperature.

A temperature in excess of 160°C (320°F) must be avoided, this may cause melt-out or yellow discoloured at these high temperatures.

The laminate quality depends on the pressure, temperature and hold time of the autoclave process. If the autoclave is not certified for the required pressure of 12 bar (175 PSI), then autoclaving can still proceed at a lower pressure, except that the hold time then has to be lengthened. The required temperature of 135 to 145°C (275 to 293°F) must be observed because the risk of faulty plies increases significantly at low autoclave temperatures.

3. Cooling

The autoclave charge is cooled down to a glass surface temperature of approx. 40°C (104°F) while the full pressure is maintained during the cooling phase. It is important that the pressure in the autoclave is only depressurized after the cooling process. If the autoclave is opened too soon while high temperatures are still prevailing, then tiny air bubbles can occur along the glass edges.

The glass temperature should be checked at different points within the autoclave as soon as the autoclave is opened. Please note, that there could be higher temperatures inside thicker glasses, although the glass surface has cooled down.

A number of maintenance and precautionary measures are recommended to ensure continuous autoclave process control, among them:

In individual cases finishing may be necessary after the autoclaved laminates have been removed. This may involve subsequent removal of PVB film exuded from the glass edges with a suitable cutting tool. Another finishing operation can be to encapsulate the windscreen edge by injection moulding of a polyurethane lip around the windscreen.

Windscreens with edge defects (edge bubbles) increase the after-pressing quota, i.e. these plies must pass through another autoclave process until complete transparency is achieveds.

Subsequent visual inspections will reveal any defects in the glass (scratches, edge splintering, inclusions, etc.) as well as defects within the sandwiched layer (inclusions, dirt, haze, optical distortions).

According to the pre-laminate production processes, windscreen edges that have not been sufficiently bonded can be subsequently treated before the autoclave frame is set up.

Such insufficient pre-laminate can be due to bending faults of the bent paired glass plies, process fluctuations, etc., and it is evident by the bubbles formed in the edge area.

Subsequent edge sealing should always be the very last possible measure and is therefore not recommended! The PVB film swells up due to the influence of a plasticiser. E.g. DOWANOL TPM (tripropylene glycolmethyl ether) is carefully applied with a roller or brush. Excessive application gives rise to the danger of autoclave fire. The most appropriate method is to apply a little fluid on the glass edge while it is still hot.

Warning: If the glass is not correctly bent then such fluids/plastiziser should not be used! Another possibility is to use clamps at points that are insufficiently edge sealed, but this method cannot be recommended, even though the bonded edges can be refinished, because there is always the risk of subsequent delamination at the clamped point after the autoclave process.

TROSIFOL products are heat sealed in bags impervious to water and water vapour. Regularly, the rolls are dispatched in vertical packaging. Roll length > 1,420 mm in horizontal packaging.

Packaging

1. Cardboard drums - vertical

Max. Width [mm]	Dimension type 2 [mm]
		Ø	Height
740	570	800
850	570	900
1000	570	1060
1150	570	1200
1320	570	1380
1420	570	1500

 

2. Cardboard boxes -vertical (4 rolls per pallet)

Max. Width [mm]	Dimension type 1[mm]
		Length	Width	Height
700	1100	1100	750
800	1100	1100	850
950	1100	1100	1000
1050	1100	1100	1100
1230	1100	1100	1260

3. Metal Boxes Reusable - horizontal

Max. Width [mm]	Length	Width	Height
1260	1420	780	985

 

 

 

The subsequent figure shows a schematic representation of the different procedures for the individual production methods. Compared to flat laminated glass, direct pressing of the loosely laid glass/film/glass sandwich with curved glasses is inappropriate to produce laminated glass that is free of entrapped air. Consequently, the autoclave process is preceded by a pre-lamination process which determines the ultimate quality of the laminated glass. A distinction in pre-nip production is made between rolls/roller press and vacuum processes. The latter is subdivided into the vacuum-bag and the vacuum-ring process.

Separating blocks cut to size are most frequently used to stack windscreen pre-laminates. The materials used for this purpose are plastics such as Nylon or Teflon. Hardwoodwedges are not advisable on account of the fact that they are flammable.

The use of so-called separating sheets is also widespread. These sheets are coated metal plates on a rigid connecting rod that holds the windscreen in a vertical position, or silicone- sheathed separating rods - as shown in the figure. However, the latter can diminish the flow of air within autoclaves and result in optical distortions in the glass plies. Direct contact between the glass and metal must be avoided on account of the different temperatures acting on the ply surface that can cause breakage. Normally the spacing between the plies should equal the ply thickness. Plies clamped too tightly in the autoclave frame to avoid glass breakage due to turbulent air can result in thin points within the film, thus causing optical faults.

Since the second half of the 1990’s laminated safety glass has been used on an increasing scale to glaze the side and rear windows. The previously described production conditions are also applicable here.

Due to the somewhat more complex glass geometry and the integration of specific functions (e.g. heating wires, antenna, etc.) vacuum pre-lamination is the preferred process for glass deairing.

Since the laminated safety glass plies have a considerably diminished glass area compared with windscreens, and due to various special features and holes for movable door glazing, the vacuum pre-lamination process (Asahi process) is the preferred option. The rubber bag process is favoured on account of the greater format diversity and the less complex bending geometry. The autoclave processes are similar to those used for windscreens of the same composition.

Testing of burglary inhibition of laminated safety glass for side and rear glazing is carried out in conformity with BS AU 209 or E DIN 52230.